The present invention relates to an apparatus for displaying a plurality of document images, and more particularly to an image display apparatus which allows, when a user searches a desired image while he/she is visually checking a number of images one by one, to sequentially display less pertinent images quickly and display more pertinent images slowly one by one.
In the past, information on papers which can be visually recognized have been stored collectively for future reference. When such information is to be retrieved, the stored information is retrieved document by document and the desired information is visually searched page by page. For example, in an office, various types of documents may be classified into files each containing 100-400 sheets. When information is to be retrieved, one of the files is taken out and the contents thereof are visually checked page by page to retrieve the desired document. Similar procedures are taken when desired information is to be retrieved from books or dictionaries. In checking the content of the real papers while manually paging the file, the speed of paging may be determined by the worker who actually pages the file. The worker does not carelessly look at the content of the document but recognizes the content of the document in synchronism with the paging.
Recently, as the volume of documents increases, it is difficult from a standpoint of storage space to store the documents in the form of paper. Methods for storing the information in a more compact manner than storing in the form of paper include a microfilming method and an electronic filing method by using magnetic disks or optical disks with computer processing as shown in "A prototype System for Electronic Storage and Retrieval of Document Images", ACM Transactions on Office Information Systems, Vol. 3, No. 3, 1985, pages 279-291. Since the documents stored in the microfilms or optical disks cannot be read by the naked eye, special display apparatus is required. The display apparatus has a function (paging function) for sequentially displaying a plurality of images so that a user can check the content page by page.
In a currently available microfilm display apparatus for a rolled film, continuous and variable speed paging can be performed. Although a user can set a speed at which the film is mechanically wound to attain continuous paging, the image flows on the display screen because of the mechanism to mechanically wind the film, and it is difficult for the user to visually check the content. Further, in the continuous paging, there is no means to indicate the boundary of pages to the user and it is difficult for the user to check the content of each page.
In backward paging using the microfilm display apparatus, the user can recognize that the film is moving backward. However, in an electronic filing system, the backward paging is performed in the same manner as forward paging and the user cannot recognize visually whether the paging is being done forward or backward.
In the paper storing system, documents are collectively stored in one place and a plurality of users search for desired documents from the collectively stored documents. This method is adopted in the electronic file display apparatus. Image data of documents are collectively stored in a central storage unit and a plurality of image display apparatus are provided to allow simultaneous retrieval of documents by a plurality of users. A plurality of users may simultaneously access the central storage unit. As the result, a waiting time from the issuance of a command for image display by the user to the actual image display may be longer than when the unit is used by one user. There has been no solution for the delay of response time when a plurality of users simultaneously access the storage unit. And there has been no means to indicate to the user that the response time will be longer than that when the unit is occupied by one user.
The problems encountered in the electronic file and the microfilm display apparatus, compared to the paper storage system, are summarized below.
(1) Since the paging is done by the display apparatus, the user has no real feeling of paging and it is difficult to check the content of each page.
(2) Even when a plurality of users simultaneously use the image storage unit, the users expect the same response time as that when the image storage unit is occupied by one user because the users are not informed that other users are using the same storage unit. As a result, the users have to wait for the display of a desired image.
(3) In the electronic file display apparatus, the displays in the forward paging and the backward paging are performed in the same manner. Accordingly, the user cannot readily recognize whether the paging is forward or backward.
(4) In the rolled film display apparatus, the user can readily recognize the direction of paging but it is difficult for the user to recognize the content because the image flows on the display screen.